This invention relates generally to a method of demulsifying water-in-oil emulsions using polyalkylene glycol derivatives. In one aspect, the method relates to the demulsification of crude oil in water emulsion.
In the production of oil from oil wells, the produced fluids frequently include water in the form of free water or emulsion. In order for the oil to be of pipeline quality, it is necessary to reduce the water content to below a specified amount (e.g. below 1.0%).
A variety of mechanical, electrical, and chemical methods are used in the dehydration of produced fluids. The present invention relates specifically to the chemical treatment using chemicals referred to as demulsifiers. A demulsifier is defined as a single or a blend of surfactant compounds in a suitable solvent system which is formulated to treat a particular emulsion on an optimum cost/performance basis. The method of the present invention employs demulsifiers for treating water-in-oil emulsions, the most common type of emulsions encountered in oil field production. It specifically excludes the treatment of oil-in-water type emulsions (i.e. reverse emulsions).
A variety of demulsifiers are known in the art, including those derived from alcohols, fatty acids, fatty amines, glycols, and alkylphenol formaldehyde condensation product.
As noted above, the method of the present invention involves the use of certain polyalkylene glycol derivatives, specif-ically adducts of a high molecular weight polyalkylene glycol and ethylene oxide and/or a diglycidyl ether.
As illustrated by the following references, polyalkylene glycol and its derivatives have been long used in the demulsification of oils.
(a) U.S. Pat. No. 4,374,734 discloses the use of polyoxypropylene polyol (mw of 2,000 to 4,500) for the breaking of water-in-oil emulsions wherein the emulsion is produced by surfactant flooding.
(b) U.S. Pat. No. 3,835,060 teaches that conventional demulsifiers include polyoxyalkylene glycol and block polymers of polyoxyethylene-polyoxypropylene.
(c) U.S. Pat. No. 2,754,271 discloses treating agents comprising an addition product of an alkylene oxide with an aliphatic dihydric alcohol and further describes the dihydric alcohol (polyoxypropylene diols) are known to have molecular weights as high as about 3,000.
(d) U.S. Pat. No. 3,557,017 discloses water-in-oil demulsifiers comprising ultra high molecular weight (of molecular weight at least 100,000) polymers. The polymers are selected from a group that includes polyoxyalkylene polymers and copolymers of monomeric alkylene oxides having a single vicinal epoxy group. Other references which disclose low molecular weight polyalkylene polyhydric reacted with other compounds include U.S. Pat. No. 3,383,326, U.S. Pat. No. 3,511,882, and U.S. Pat. No. 3,676,501. Other references which disclose polyhidric alcohols but not glycols include U.S. Pat. No. 2,996,551, U.S. Pat. No. 3,078,271, and U.S. Pat. No. 4,305,835.